1. Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente. Reserve 1 cup of pasta water before draining.2. While pasta cooks, heat olive oil in a large, deep skillet over medium-high heat. Add the Italian sausage (casings removed). Cook, breaking it apart with a spoon, until browned and cooked through, about 5-7 minutes.3. Do not drain the fat. Add the diced onion to the skillet with the sausage fat. Sauté for 3-4 minutes until softened.4. Add the minced garlic and red pepper flakes. Cook for 1 more minute until fragrant.5. Add the broccoli florets and the chicken broth. Stir to combine.6. Bring the broth to a simmer, then cover the skillet. Let the broccoli steam for 3-5 minutes, until tender-crisp.7. Uncover the skillet. Add the cooked, drained pasta to the skillet along with the grated Parmesan and 1/2 cup of the reserved pasta water.8. Stir everything together vigorously for 1-2 minutes, allowing the sauce to thicken and coat the pasta. If it seems dry, add more pasta water.9. Season with salt and pepper to taste. Serve immediately.